This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 199 15 082.6 filed on Apr. 1, 1999, the entire disclosure of which is incorporated herein by reference.
The invention relates to a nozzle and a method for producing a nozzle for a rocket engine, whereby the nozzle is produced in such a way that it can be regeneratively cooled by means of a coolant flowing through tubular passages in the nozzle wall.
Nozzles of rocket engines are parts which are subjected to extreme thermal loads calling for special measures to assure their stability during operation of the rocket engine. One option for such a measure involves regenerative cooling of the nozzle by means of a coolant which is conducted through the nozzle body under pressure. In the case of liquid propellant rockets a possible coolant is one of the fuel components. Thus for example in a rocket engine which uses hydrogen as a fuel, prior to supplying the hydrogen to the combustion chamber, it may be conducted through the nozzle body to cool the nozzle. In a rocket engine naturally the saving of any additional weight is of considerable importance. Therefore, it is a particular aim to produce a regeneratively cooled nozzle so that it combines high strength with a light weight.
German Patent Publication DE 43 26 338 C2 discloses nozzles for rocket engines, which nozzles are regeneratively cooled by a flowing coolant. The known nozzle body is produced by winding a tubular material onto a winding mandrel. Coolant can flow through the tubular material during operation of the nozzle. The wound tubular material forms a helical structure or body in which the individual turns are stabilized by welding the turns together on the xe2x80x9ccoldxe2x80x9d or exterior side of the wound helical body. A tubular material of rectangular cross-section is used so that the surface of the interior of the spiral composite structure forming the nozzle body is essentially smooth. The welding operation leaves room for improvement because very long welding seams are required and damage to the tubular cross-sectional flow area may occur.
German Patent Publication DE 39 42 022 C2 (Herzog et al.) discloses a cooling system for turbo-jet engines. Coolant flows through channels in engine component walls. Boundary layer air is liquified and vaporized for use as the coolant.
German Patent Publication DE 197 16 524 C1 (Huber et al.) discloses an aluminum alloy and a magnesium alloy that is water soluble and can be used, for example, for the present fixing layer to be described below.
German Patent Publication DE 195 20 885 C2 (Voggenreiter et al.) discloses a method for thermal spraying of a load bearing heat resistant layer. Such spraying method and the materials disclosed by Voggenreiter et al. are useful for the present purposes.
German Patent Publication DE 27 43 838 (Farfaglia) is based on U.S. Ser. No. 727,910 filed in the U.S. on Sep. 29, 1976, now U.S. Pat. No. 4,131,057 which discloses an apparatus for winding tubular material onto a mandrel for producing a tubular wall of a container.
German Patent Publication DE 31 19 712 C2 (Donguy) discloses a connector for securing components of a solid fuel rocket engine to each other.
In view of the above it is the aim of the invention to achieve the following objects singly or in combination:
to construct the nozzle body in such a way that it has a reduced weight compared to conventional nozzle bodies of this type and size while simultaneously having an improved strength, to withstand a high pressure of a cooling medium flowing through the nozzle body in operation;
to improve the heat resistance of a regeneratively cooled nozzle while simultaneously forming a smooth radially inwardly facing nozzle surface contacted by the combustion flow in operation;
to avoid time and extra material consuming efforts such as welding operations in the nozzle production;
to provide the nozzle body on its interior with a heat resistant, load supporting layer;
to provide the nozzle body, especially at its ends, with reinforced areas for flanging the nozzle body to a compensation chamber or the like;
to disclose an improved method for producing a nozzle for a rocket engine, whereby the nozzle shall be regeneratively coolable by a coolant flowing through the nozzle body; and
to provide a regeneratively coolable nozzle for a rocket engine, said nozzle comprising the above outlined improved characteristics.
According to the invention, a method for producing a regeneratively coolable nozzle or nozzle body for a rocket engine, comprises the following steps:
winding tubular material onto a winding spindle or mandrel in the form of a helical composite nozzle body structure, whereby the tubular material is capable of having a coolant flown therethrough during operation of the nozzle;
fixing the spiral composite nozzle body structure to retain its helical nozzle body structure at least temporarily;
removing the fixed composite structure from the winding spindle or mandrel; and
applying a heat resistant load bearing layer to the radially inwardly facing surface of the fixed composite nozzle body structure forming the hot-gas side of the nozzle body.
The method according to the invention provides a significant advantage in that the nozzle so produced, while being very lightweight, withstands a high coolant pressure which may be within the range of about 200 to 250 bar. Moreover, the material heat resistant load bearing layer has a smooth surface facing the hot-gas flowing through the nozzle body, whereby the flow characteristics are improved.
It is advantageous if application of the heat resistant load bearing layer is by a spraying method.
It is particularly advantageous if the application of the heat resistant, load bearing layer takes place by flame spraying such as a high velocity oxygen fuel (HVOF) method. The high velocity oxygen fuel method provides the advantage of making it possible to produce stable load bearing layers having a low porosity and a low oxygen content.
Alternatively, application of the load bearing layer can take place by vacuum plasma spraying or by cold-gas spraying.
According to a particularly advantageous embodiment of the method according to the invention, fixing of the individual turns of the tubular material in the shape of the helical composite nozzle body structure takes place after winding the tubular material turns onto a mandrel. A removable external fixation layer is applied to the exterior of the spiral composite nozzle body structure, whereby the turns of the tubular material are temporarily held in place in a simple way without any time consuming, expensive or material-weakening measures such as welding together the tubular material turns. After the internal heat resistant load bearing layer has been applied and set, the external fixation layer is removed.
Advantageously, the fixation layer is formed by spray application of the layer material, such as a water-soluble alloy, whereby AQUALLOY is of particular advantage due to its easy removability.
As alternatives, the external, temporary fixation layer can be formed of a gypsum material, a low-melting metal, or a low-melting metal alloy. These materials are also easily removed.
If the fixation layer is removed after producing the load bearing layer it is assured that the turns of the tubular material will retain their position within the nozzle body since those turns are now held in place by the heat resistant, load bearing layer.
Preferably, a finishing operation is applied to the load bearing layer to increase the smoothness of the radially inwardly facing surface of the load bearing layer. In this way the surface of the hot-gas wall, which after application is already quite smooth, can further be improved in its surface finish for assuring an improved flow of the hot gases through the nozzle.
According to a development of the method according to the invention, a further heat resistant, load bearing layer is applied in the area of the ends on the outside of the spiral composite nozzle body structure to create connecting flange areas which provide the advantage of flange-mounting the nozzle body to the combustion chamber structure or of flanging propulsion plant components to the nozzle body in a simple and economical way. Preferably, this further load bearing layer is applied after removal of the fixation layer.
According to a development of the method according to the invention, the production of the load bearing layer or layers is followed by an annealing treatment of the spiral composite structure.
Preferably, the tubular material used for winding the spiral composite structure is of rectangular cross-section, in particular of square cross-section with outer surfaces that preferably bulge radially outwardly. This feature is produced by pressurizing the helical composite nozzle body structure by introducing a medium at high pressure within the range of about 300 to 350 bar into the tubular material for bulging outer walls of the tubular material radially outwardly. In this way the tubular material assumes a shape in which it will be able to withstand high operational pressures without any further plastic deformation. Incidentally, the bulging operation is performed after the wound body of tubular material has been annealed.
The nozzle body according to the invention is characterized by a helically wound structure of a tubular material which is reinforced by a radially inwardly facing heat resistant load bearing layer, preferably made of special, high grade steel, nickel chromium alloys such as Inconell 800(copyright) or other materials known to withstand loads under high temperature conditions prevailing in an operating rocket engine. This heat resistant load bearing layer is smooth on the inwardly facing surface for improved flow conditions.
Further load bearing layers outwardly applied to at least one outer end surface area of the nozzle body provide flanging areas in a simple and economical way for connection to the combustion chamber or to other components of the rocket engine.